The effect of replacing the anion from N to Bi down the group in the periodic table is investigated on SrMg2X2 (X =N, P, As, Sb, Bi). A full potential linearized augmented plane wave plus local orbitals method is used along with different exchange–correlation potentials to obtain the lattice constants, phonons, electronic, and optical properties of the SrMg2X2 (X =N, P, As, Sb, Bi) Zintl compounds. A good agreement is achieved and our calculations are validated by previous experimental and theoretical data. All compounds have shown stable dynamical behavior with gamma centered longitudinal response having no imaginary frequencies. Electronic band structures reveal the semiconducting nature of the compounds. The Pnictogen (X )-p state contributed mainly in the valence band and the Sr-d state forms the conduction of the compounds. Relative charge transfer and low overlapping of the atomic densities indicates the preferable ionic bonding character of these materials. In the optical properties, real and imaginary parts of dielectric function, complex refractive index, birefringence, reflectivity, and optical conductivity are calculated. These compounds can be utilized in the optical and optoelectronic devices.